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Asesoramiento nutricional para mejorar los resultados en los embarazos múltiples

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Resumen

Antecedentes

Los embarazos múltiples se asocian con tasas más altas de mortalidad y morbilidad perinatal que los embarazos únicos, debido principalmente a un aumento del riesgo de parto prematuro. Debido a que el resultado fetal es mejor en un rango particular de incremento del peso materno, se ha indicado que las mujeres con embarazos múltiples deben recibir dietas especiales (en particular dietas altas en calorías) diseñadas para estimular el aumento de peso. Sin embargo, “el aumento de peso óptimo” en la madre en los estudios retrospectivos solamente puede reflejar un buen crecimiento de los fetos y un parto a término o casi a término (ambos asociados con un buen resultado), y es posible que el estímulo artificial del aumento de peso mediante el aporte nutricional no confiera ventajas. En efecto, puede ser desagradable consumir una dieta hipercalórica, y podría dar lugar a problemas de sobrepeso a largo plazo. Por lo tanto, es importante establecer si las dietas especializadas en realidad son beneficiosas para las mujeres con embarazos múltiples y sus recién nacidos.

Objetivos

Evaluar los efectos de las dietas especializadas o el asesoramiento nutricional para las mujeres con embarazos múltiples (dos o más fetos).

Métodos de búsqueda

Se hicieron búsquedas en el Registro de Ensayos del Grupo Cochrane de Embarazo y Parto (Cochrane Pregnancy and Childbirth Group) (15 de junio 2015).

Criterios de selección

Ensayos controlados aleatorizados, estudios “cuasialeatorizados”, y ensayos aleatorizados grupales de mujeres nulíparas o multíparas con embarazos múltiples (dos o más fetos) y sus recién nacidos. Los ensayos cruzados (cross‐over) y los estudios informados solo como resúmenes no fueron elegibles para la inclusión.

Obtención y análisis de los datos

No se identificaron ensayos para su inclusión en esta revisión.

Resultados principales

Una búsqueda exhaustiva del Registro de Ensayos del Grupo Cochrane de Embarazo y Parto no encontró informes de ensayos potencialmente elegibles.

Conclusiones de los autores

No hay evidencia consistente a partir de ensayos aleatorizados para indicar si las dietas especializadas o el asesoramiento nutricional para las mujeres con embarazos múltiples causan más efectos beneficiosos que daños. Existe una necesidad clara de realizar un ensayo controlado aleatorizado.

PICO

Population
Intervention
Comparison
Outcome

El uso y la enseñanza del modelo PICO están muy extendidos en el ámbito de la atención sanitaria basada en la evidencia para formular preguntas y estrategias de búsqueda y para caracterizar estudios o metanálisis clínicos. PICO son las siglas en inglés de cuatro posibles componentes de una pregunta de investigación: paciente, población o problema; intervención; comparación; desenlace (outcome).

Para saber más sobre el uso del modelo PICO, puede consultar el Manual Cochrane.

Asesoramiento nutricional para mejorar los resultados en los embarazos múltiples

En los embarazos múltiples (gemelos, trillizos y más) la tasa metabólica de la madre es mayor que en las mujeres con embarazos con un feto único, por lo que una dieta hipercalórica también puede ayudar a mantener el estado nutricional de la madre. Los embarazos múltiples presentan un riesgo mayor de complicaciones para las mujeres y sus recién nacidos que los embarazos únicos. Específicamente, el crecimiento deficiente del feto en el útero, el parto prematuro y el peso bajo al nacer son las más frecuentes.

Se ha indicado que una dieta hipercalórica especial para la mujer embarazada podría mejorar los resultados para los recién nacidos. Sin embargo, es posible que el impulso artificial del aumento de peso no proporcione ventajas y podría ser desagradable para la madre. Incluso puede contribuir con problemas de sobrepeso a largo plazo para la mujer. Esta revisión Cochrane tuvo como objetivo identificar estudios controlados de calidad que compararan dietas especiales con dietas normales, o ensayos que consideraran el asesoramiento sobre dietas especiales, pero no se encontraron. Es decir, no hay evidencia a partir de ensayos aleatorizados para indicar si el asesoramiento nutricional específico para las mujeres con embarazos múltiples causa más efectos beneficiosos que daños.

Authors' conclusions

Implications for practice

This review shows that there is no evidence from randomised trials to support, or reject, special diets or special nutritional advice for women with multiple pregnancies. The optimal diet for women with multiple pregnancies is uncertain.

Implications for research

Future research should focus on designing a suitable randomised trial comparing a special high‐calorie diet with usual diet. As well as assessing clinical outcomes (notably preterm birth and small‐for‐gestational age), such a trial should address maternal views and long‐term weight profile.

Background

Description of the condition

Multiple pregnancies occur when two or more fetuses are present in the uterus; this can be a result of implantation of two genetically different fertilised eggs by two different sperm (dizygotic twins), or due to the division of one fertilised egg (monozygotic). Monozygotic twins can share the same placenta (monochorionic) or have separate placentas (dichorionic) (Fox 2006).

Multiple pregnancies can be diagnosed by an ultrasound scan as early as six weeks. Women with multiple pregnancies may have more severe nausea and vomiting than those with singleton pregnancies, as a result of higher levels of human chorionic gonadotropin (hCG) (Rao 2004).

Since the 1970s there has been a steady increase in the number of twin pregnancies; from 9.6 per 1000 maternities in England and Wales (ONS 2006) in 1976 to 15.5 in 2008 (ONS 2009); in the USA, 18.8 per 1000 were twins in 1975 (Taffel 1992) rising to 32.1 per 1000 in 2006 (Martin 2009), while in Australia in 2010 multiple births accounted for 3.1% of all births (Umstad 2013). These trends have been reflected in many settings across the globe. This rise has been attributed to the increase in the use of assisted reproductive technology, and to some women deciding to have children later in life. An increase in maternal age increases the chances of multiple pregnancy. In the USA it was found that 20% of twin pregnancies from 1980 to 1997 were due to spontaneous conception, 40% due to in vitro fertilisation and 40% due to ovulation induction (Nakhuda 2005). In Europe, spontaneously conceived twins comprise 1% of all deliveries; 20% to 30% of all twins are due to assisted reproductive technology (Hansen 2009), although recent policies to restrict the number of embryos transferred during assisted conception may reverse the upward trend in multiple pregnancies (Collins 2007; Umstad 2013).

Multiple pregnancies are associated with higher rates of complications for both the mother and the fetuses. Gestational hypertension and pre‐eclampsia are twice as likely to occur with twins as in singleton pregnancies with risk ratios of 2 and 2.6 respectively (Siddiqui 2007). There is a higher incidence of antepartum and postpartum haemorrhage, with the average blood loss after delivery being 500 mL higher than after a singleton birth (Rao 2004).

Mulitple births have a substantial perinatal mortality rate (PMR) compared to singletons. In England and Wales, in 2006, there was an overall PMR of 8.2 per 1000 births, with twins having a rate of 27.2 per 1000, and triplets and higher order births 81.8 per 1000 (CEMACH 2008). When infants are born long before term they are functionally immature, and are usually admitted to neonatal intensive care units. They have poor thermoregulatory mechanisms, which are worsened by low brown fat levels and heat loss. Respiratory distress syndrome occurs as a result of lack of surfactant, and may be associated with chronic lung disease (bronchopulmonary dysplasia) (Keeling 2000). Multiple pregnancies have a strong association with preterm deliveries (before 37 weeks), ranging from 48.2% in Ireland to 68.4% in Austria; between 39.1% and 47.1% occur at 32 to 36 weeks, and 8.1% to 12.7% before 32 weeks (Blondel 2006).

Fifty per cent of twins are small‐for‐gestational age (SGA) by 39 weeks using the 1991 US singleton live birth values. Ten per cent to 15% of multiple pregnancies (twins and triplets) are SGA by 22 to 30 weeks' gestation (Alexander 1998).

Cerebral palsy is also eight times more likely to occur in twins, and has a greater prevalence when the birthweight is less than 1000 g (Pharoah 2002). When infants are below 1500 g, 30% to 65% will have neurological problems ranging from motor to cognitive/behavioural deficits. Other severe neurological concerns are intraventricular haemorrhage and periventricular leukomalacia. Necrotising enterocolitis also affects low birthweight infants, and there is a high risk of infection due to an immature immune system. Prematurity is a risk factor for retinopathy of prematurity; the retina is vascularly immature as there is insufficient vascularisation due to poor production of angiogenic factors (Keeling 2000).

Depending on the chorionicity of the twins, there are specific complications. For example, 10% to 15% of monochorionic twins have twin‐twin transfusion syndrome which can result in fetal death if left untreated. This occurs as a result of anastomoses (a connection between two blood vessels) on the placenta, resulting in a compromise of blood flow to one of the twins, which results in poor growth while the other twin receives the redirected blood from the placenta (Rao 2004).

The risk to mother and fetus is increased even more when the number of fetuses increases. High order pregnancies such as triplets and quadruplets have higher rates of perinatal mortality and have an earlier gestation at delivery; the average gestation for triplets is 33.4 weeks. High order births are more likely to deliver earlier on in the pregnancy than twins; 16.9% of triplets and 29.2% of quadruplets were born before 29 weeks compared to 5.6% of twins. The risk of complications is also greatly increased for higher order births with rates of cerebral palsy of 31/1000 reported for triplets (Bromer 2011).The number of fetuses also impacts on the chances of survival for both twins, with 6.3% of triplet and 8.0% of quadruplet pregnancies having one or more fetal deaths compared to 2.4% of twins (Luke 2008).

In one series, 100% of triplets were admitted to the neonatal intensive care unit, and 54% had a major morbidity (retinopathy of the newborn, necrotising enterocolitis, ventilator support or intraventricular haemorrhage) (Luke 2006).

Description of the intervention

It has been suggested that improved diets may lead to improved outcomes in multiple pregnancies. This is based on observations that a particular range of maternal weight gain is optimally associated with good fetal outcome (Goodnight 2009). However, the converse is not necessarily true ‐ that outcome can be improved by boosting maternal weight gain through improved diet.

Dietary input consists of many different components that may be relevant to multiple pregnancy. These include quantity of calorific intake, the source of calories such as a fat or proteins, micronutrients such as vitamin C, vitamin E, thiamine, magnesium, calcium and zinc, as well the inclusion of certain nutrients such as omega fats. The balance and amount of these components have the potential to impact on the health of the mother and fetuses.

Detailed dietary advice has been popular in the US. For example, Luke et al recommend a calorie intake of 4000 kcal for underweight mothers (body mass index (BMI) 19.8) with a total weight gain of 50 lbs to 62 lbs (23 to 28 kg); 3500 kcal for normal weight (BMI 19.8 to 26.0) with a weight gain of 40 lbs to 54 lbs (18 to 25 kg); 3250 kcal for overweight (BMI  26.1 to 29.0) 38 lbs to 47 lbs (17 to 21 kg); and 3000 kcal for obese mothers (BMI greater than 29.0) with a weight gain of 29 lbs to 38 lbs (13 to 17 kg) (Luke 2005).

The Institute of Medicine in the US has produced guidelines recommending a weight gain of 37 lbs to 54 lbs (17 to 25 kg) for normal weight, 31 lbs to 50 lbs (14 to 23 kg) for overweight, and 25 lbs to 42 lbs (11 to 19 kg) for obese women (Rasmussen 2009).

Published work also discusses the importance of a high carbohydrate diet as it has been linked to unwanted weight gain, poor glycaemic control and poor fetal growth, whereas a diet consisting of 20% protein, 40% carbohydrate, and 40% fat was found to have better fetal growth (Luke 2005).

Haematinic supplements such as folic acid and iron will not be considered in this review, as they are assessed elsewhere (Peña‐Rosas 2015a; Peña‐Rosas 2015b).

How the intervention might work

In multiple pregnancies, the metabolic rate of the mother is 10% greater than in women with singleton pregnancies (Shinagawa 2005), as a result of an increasing demand on the mother’s energy expenditure due to a larger placenta producing higher quantities of hormones, and two fetuses requiring a continuous nutrient supply for growth (Goodnight 2009). As a result of the increased energy use, fasting glucose levels are lower with a resulting depletion of glycogen reserves. Fats are broken down as an alternative energy source (Luke 2005).

The theoretical basis for recommending high‐calorie diets is to increase the provision of nutrients to prevent the likelihood of poor fetal growth. Poor fetal growth may have a number of adverse consequences and can also be associated with preterm birth. A high‐calorie diet may also help maintain the mother's nutritional state, which otherwise may be depleted by the needs of the babies, resulting in impaired maternal sense of well being. A retrospective study has shown that women with normal weights at the start of twin pregnancies are more likely to have larger neonates and less likely to deliver preterm if their weight gain during pregnancy met US Institute of Medicine recommendations (Fox 2010).

Although the focus has been on high‐calorie diets, any trial of any nutritional intervention (e.g. overall better quality) specifically tailored for women with multiple pregnancies would be of interest.

Why it is important to do this review

Some recommended diets for women with multiple pregnancies have calorific contents similar or greater than those for frontline troops (e.g. 4000 kcal daily for British troops in Afganistan; HM Forces 2011). As some women with multiple pregnancies are more sedentary than they would be when not pregnant, these diets have the potential to be associated with substantial weight gain. Excess weight gain is associated with increased complications in labour and higher rates of caesarean births, gestational diabetes, pre‐eclampsia and anaesthesia‐related risks (Reece 2008). Obese mothers have higher rates of fetal macrosomia, as well as increased chance of infection post surgery. By advocating a high‐calorie diet and a high weight gain it is important to consider the psychological impact this might have on the mother as well as future implications for her health. The mother will then have to face the difficulty of losing her extra weight postpartum, as obesity is linked to type 2 diabetes, cardiovascular disease, and thromboembolism (Castro 2002). It therefore needs to be established whether special diets do lead to improved outcomes for the babies and whether these cause unwanted weight gain in the mother.

In addition, a woman might experience anxiety if she were unable to follow specific nutritional advice, because of worry about resulting harm to her babies.

It is also important to consider the financial implications, as a high‐calorie diet may be expensive.

Objectives

To assess the effects of special diets, or dietary advice, on the outcome of multiple pregnancies.

Methods

Criteria for considering studies for this review

Types of studies

Randomised controlled trials; 'quasi‐random' studies, and cluster‐randomised trials are eligible for inclusion. We planned to exclude cross‐over trials and studies presented only as abstracts.

Types of participants

Women with multiple pregnancies (two or more fetuses) either nulliparous or multiparous, and their babies.

Types of interventions

Specialised diets or specific dietary advice for multiple pregnancies, whether or not demonstrated to have an impact on weight gain during pregnancy, compared with usual care or alternative diets/advice.

Types of outcome measures

Primary outcomes

  1. Early preterm births (before 34 weeks)

  2. Small‐for‐gestational age (SGA) at birth (as defined by the trialists)

Secondary outcomes
Maternal outcomes

  1. Weight gain

  2. Caesarean births

  3. Instrumental vaginal delivery

  4. Maternal satisfaction/dissatisfaction/anxiety

 Fetal outcomes

  1. Preterm birth less than 37 weeks

  2. Very early preterm birth less than 28 weeks

  3. Respiratory distress syndrome

  4. Intraventricular haemorrhage

  5. Periventricular leukomalacia

  6. Retinopathy of prematurity

  7. Necrotising enterocolitis

  8. Admission to neonatal intensive care unit

  9. Perinatal death

Child outcomes

  1. Learning difficulties

  2. Developmental delay (as defined by the trialists)

  3. Growth (weight, head circumference, height/length)

  4. Cerebral palsy

Search methods for identification of studies

The following methods section of this review is based on a standard template used by the Cochrane Pregnancy and Childbirth Group.

Electronic searches

We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register by contacting the Trials Search Co‐ordinator (15 June 2015).

The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from:

  1. monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);

  2. weekly searches of MEDLINE (Ovid);

  3. weekly searches of Embase (Ovid);

  4. monthly searches of CINAHL (EBSCO);

  5. handsearches of 30 journals and the proceedings of major conferences;

  6. weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.

Details of the search strategies for CENTRAL, MEDLINE, Embase and CINAHL, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.

Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co‐ordinator searches the register for each review using the topic list rather than keywords.

Searching other resources

We planned to search the reference lists of retrieved articles.

We did not apply any language or date restrictions.

Data collection and analysis

For methods used in the previous version of this review, seeBallard 2011.

No new reports were identified as a result of the updated search.

If any relevant reports are identified in future updates of this review we will use the methods set out in Appendix 1.

Results

Description of studies

Results of the search

The search of the Cochrane Pregnancy and Childbirth Group's Trials Register found no trial reports.

Risk of bias in included studies

We were unable to include any studies in this review.

Effects of interventions

We were unable to establish the effectiveness of nutritional advice as no randomised controlled studies were found.

Discussion

Summary of main results

Using the above search methods and strategies, we found no trials.